I keep coming up against this error, sometimes I manage to get rid of it through hours of tinkering, but still have not found out why it comes up. On theis new site i'm working on, i just can't get rid of it period.

That error usually means something is out of scope of the code trying to work with it, such as the pics not being present when that code executes, possibly being somewhere down a timeline. There are other possible reasons as well, such as misnaming an instance.

If you go to your Publish Settings, in the Flash section there is an option to Permit debugging. If you select that option your error message may also point to a line number following the frame indication.